According to a new NASA study, Arctic perennial sea ice has been decreasing at a rate of 9 percent per decade since the 1970s. The changes in Arctic ice may be a harbinger of global climate change, says Josefino Comiso, researcher at Goddard Space Flight Center, in Greenbelt, Maryland. In a recent Journal of Climate paper, Comiso notes that most of the recent global warming occurred over the last decade, with the largest temperature increase occurring over North America. Researchers suspect the loss of Arctic sea ice may be caused by changing atmospheric pressure patterns over the Arctic that move sea ice around, and by warming Arctic temperatures that result from the buildup of greenhouse gases in the atmosphere. (Click to read the NASA press release.)

The image above shows a comparison of composites over the Arctic Circle, acquired in 1979 (top) and 2003 (bottom) by the DMSP Special Sensor Microwave Imager (SSMI). The first image shows the minimum sea ice concentration for the year 1979, and the second image shows the minimum sea ice concentration in 2003.